Depending upon the kind of an external device in which a secondary battery is used, the secondary battery may be configured to have a detachable type structure in which the secondary battery can be easily inserted into and removed from the external device or to have an embedded type structure in which the secondary battery is embedded in the external device. For example, the secondary battery can be inserted or removed into or from devices, such as laptop computers, as needed. On the other hand, devices, such as some kinds of mobile phones, MPEG Audio Layer-3 (MP3) players, tablet PCs, and smart pads, require an embedded type battery pack due to the structure or capacity thereof.
Meanwhile, various kinds of combustible materials are contained in a lithium secondary battery, which has been increasingly used in recent years. As a result, the lithium secondary battery may be heated or explode due to overcharge of the lithium secondary battery, overcurrent in the lithium secondary battery, or other external physical impact applied to the lithium secondary battery. That is, the safety of the lithium secondary battery is very low. Consequently, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), for effectively controlling an abnormal state of the lithium secondary battery, such as overcharge of the lithium secondary battery or overcurrent in the lithium secondary battery, are connected to a battery cell.
Preferably, the secondary battery is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which has a small weight to capacity ratio, is usually used as a battery cell of the secondary battery. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, since the pouch-shaped battery is lightweight and the manufacturing cost of the pouch-shaped battery is low.
When a battery module or a battery pack is manufactured using pouch-shaped batteries as described above, however, various difficulties and problems are caused during connection between electrode terminals of the pouch-shaped batteries by welding. In addition, a pouch-shaped battery case has an advantage in that the pouch-shaped battery case easily cracks when external impact is applied to the pouch-shaped battery case, for example the pouch-shaped battery case drops or vibrates, due to the structural characteristics of the pouch-shaped battery case.
In order to solve the above problems, research has been conducted into a structure in which a cell cover is mounted at the top and bottom of a pouch-shaped battery cell, a structure in which a cartridge for fixing a pouch-shaped battery cell is used, and a structure in which two or more battery cells are connected to each other using an adhesive tape. In these structures, however, the number of parts is increased with the result that manufacturing cost is increased and a manufacturing processability is lowered. In addition, the volume of the battery pack or the battery module in which the pouch pouch-shaped battery cells are connected is increased.
Consequently, there is a high necessity for a battery pack having a compact structure and exhibiting structural stability while solving the above problems. In addition, there is a high necessity for a battery pack having a large capacity to size ratio according to a trend of miniaturizing and thinning a device.